It’s simple: business investments go into products that matter to profits. The Mac Pro is almost an irrelevancy at this point, contributing perhaps 1% of Apple’s sales, with iPhone and iPad dominating the lineup, and laptops after that.

Add in the resources required to release a rumored iPhone 5 next month and to bring Lion to fruition, and one can reasonably assume that a revised Mac Pro is quite irrelevant to Apple. In fact, Apple could drop it entirely and hardly notice.

Now add in the fact that there is no new chipset (e.g., no “Sandy Bridge” Intel chipset) that would make a new Mac Pro compelling, and the picture is complete.

Could it be Spring 2012 before we see a new model? If we don’t see a new model announced within a few weeks, I deem a February/March date much more likely. Anything sooner is likely to be an incremental update rather than something substantial.